I browsed around a bit and don't fully agree; there appear to be quite a few legit/harmless interest groups. But also a pretty good sprinkling of, as you say, alt-right; for example under "atheism" one group (not the largest by a lot) is the "Anti-SJWs". Under "skepticism" the second-largest appears to be anti-vax excuse me skeptical about vaccinations.

Disappointed that I see no way to read a group's posts without joining the group.